Bulletin d’avalanche

Banner Summit

Sawtooth Avalanche Center
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Danger d’avalanche

Sun
Alpin
3 · Marqué
Limite forestière
2 · Modéré
Sous la limite
1 · Faible
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Périmé — ce bulletin a expiré 7 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Triggering an avalanche is likely today in areas with fresh drifts of wind transported snow. Buried weak layers remain capable of producing avalanches big enough to bury or injure a person. These could be triggered from gentle or flat terrain above, below, or to the sides of steep slopes. Conditions warrant a conservative approach: choose lower-angled slopes and avoid terrain with nasty consequences.

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–2

    Our snowpack has several persistent weak layers; the most notable is a layer of surface hoar buried 1.5-2 feet deep. This layer is remarkably widespread and exists on almost all mid and upper elevation slopes. Our lamentable lack of snowfall has given these weak layers a breather, but triggering a dangerous avalanche remains possible. Take a hard look at the photo to the right—is this the sort of snowpack you want underfoot?

    Just when you start to let your guard down, these weak layers often have a few more tricks up their sleeves. Yesterday, skiers on Galena Summit triggered a small persistent slab avalanche on a steep roadcut (see photo in Media), an indicator that a larger avalanche is possible on the right—or wrong—slope. Most local avalanche professionals are continuing to choose lower angled slopes, and some are avoiding avalanche terrain all together. While not a glamorous approach to managing the persistent slab problem, it's the only sure-fire way of staying out of trouble.

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1

    Yesterday's increasing northerly winds easily transported the low-density fluff left over from the Christmas eve storm. Many field observers reported snow billowing from high elevation ridges, and Ben found some small, but touchy, wind slabs yesterday afternoon in the high Smoky mountains. At upper elevations today, avoid areas with the tell-tale signs of freshly wind-loaded slopes: pillowed drifts, dune-like formations, or a rippled surface texture. These wind slabs will remain sensitive today and are adding additional weight to the weak layers described above.

Avalanche Discussion

Our snowpack has several buried weak layers, including weak, sugary snow at the base of the snowpack and a layer of surface hoar that was buried on December 7th. It's not the sort of snowpack that gets me fired up to go ride steep lines.

Of our persistent weak layers, the surface hoar layer buried 1-2 feet deep has received the most attention. It produced the majority of avalanche activity back in mid-December, and was responsible for the most recent human-triggered slides—including the large avalanche remotely-triggered by Sun Valley Heli Ski on December 22nd, and possibly the small slide triggered yesterday on Galena Summit. What's remarkable is just how widespread this layer is. On Christmas, Ethan found it in the Soldier Mountains. The next day I found it in Baker Creek 20 miles away. Yesterday I was in the mountains NW of Stanley where I found nearly identical snowpack layering, and this is a whopping 60 miles from Ethan's observation! Like clockwork, almost every snow pit—whether dug by us or others—shows a very similar snowpack.

The upside is this: you don't have to guess at the snowpack under your sled or skis. There's a 95% chance that the buried weak layers exist beneath you. The question is whether or not you will trigger them, and there's no way to know that answer for sure. Seasoned avalanche professionals that have seen a lot of nasty weak layers in their day, and seen these act in unpredictable ways, have concluded that as long as these layers exist—especially the surface hoar—the best approach is to assume the worst. 

Régions couvertes